The present invention generally relates to a photographing apparatus, an image processing method, and a recording medium for recording an image processing program. More specifically, the present invention is related to such a photographing apparatus as a digital camera equipped with an optical zooming function, an image processing method employed in the digital camera, and a recording medium for recording thereon the image processing program, capable of improving contrast characteristics deteriorated in zooming magnification.
Among photographing apparatus such as digital cameras, some photographing apparatus are equipped with optical zooming functions. This optical zooming function corresponds to such a function that since a lens optical system is moved, a focal distance of this lens optical system is physically changed so as to be capable of changing an enlarging ratio of an image.
Conventionally, in a photographing apparatus equipped with such an optical zooming function, a contrast characteristic of a photographed image acquired at a wide terminal (wide angle side, namely under condition that focal distance becomes “shortest”) is different from a contrast characteristic of a photographed image acquired at a telescopic terminal (telephotograph side, namely under condition that focal distance becomes “longest”). In particular, when zooming magnification becomes high, namely at the telescopic terminal (telephotograph side), a photographed image owns no contrast feeling, and therefore, is brought into such an image condition that a black image portion of this photographed image is floating. Such a phenomenon that a contrast feeling disappears is referred to as a “flare.” This “flare” phenomenon is caused by lens characteristics of an optical system.
Very recently, since compact digital cameras are commercially available, there is such a trend that optical lenses mounted on these digital cameras are manufactured in smaller sizes. As a result, when zooming magnification is increased, the following problem may occur. That is, since the above-explained “flare” phenomenon is increased, contrast characteristics are considerably deteriorated.
In this connection as a method for correcting a brightness of an image, there is a method for controlling an exposure during a photographing operation. For instance, Japanese Laid-open Patent Application No. Hei-7-274062 discloses the following image exposure correcting method. That is, since the diaphragm/shutter mechanism is controlled in such a manner that the exposure amount obtained when the maximum Y signal (maximum luminance signal) is acquired may be nearly equal to 70 to 100% of the dynamic range of the CCD, the exposing control operation can be properly carried out under such a condition that a light photographic object may become lighter, whereas a dark photographic object may become darker.
However, the brightness correcting method described in the above-explained patent publication merely corresponds to an exposure correcting method. As a consequence, even though the brightness of the entire image can be adjusted, this brightness correcting method cannot avoid that the above-described contract characteristic is deteriorated due to the zooming magnification.
It should be understood that as a method capable of correcting a brightness of a photographed image, for instance, there is such a method for using specific software installed in a personal computer. However, this brightness correcting software method owns other problems, namely requirements of very cumbersome works. That is, a user is necessarily required to acquire photographed images into the personal computer. Also, while the user must confirm the brightnesses of the photographed images on the display screen, the user is required to fine-adjust the contrast of these confirmed images by performing a predetermined contrast adjusting operation in the manual manner.